From 19.20.21:

"The rise of supercities is the defining megatrend of the 21st century. In 1800 less than 3% of the world lived in cities. In 1900 150 million people lived in the world's cities. More than half the people on Earth now live in cities."

We all know rapid changes are occurring in the way people live and interact with their environment and each other. What fascinates me is the little details. This post on The Year in Pictures blog has photos of people in Shanghai wearing pyjamas as outdoor clothing. Here's the book in which the photos appear over on Amazon, it's called Planet Shanghai by Justin Guariglia.